The structures of Ag55+ and Ag55- : trapped ion electron diffraction and density functional theory.

We report the experimental structure determination of cold, mass selected Ag(55)(+/-) cluster ions using the recently developed technique of trapped ion electron diffraction. By comparison of experimental and theoretical molecular scattering functions and consideration of computed total energies, we show that Ag(55)(+) constitutes an ideal Mackay icosahedron, whereas Ag(55)(-) is a weakly Jahn-Teller distorted icosahedron. Isomers of other structural types, for example, decahedral or close-packed, could be ruled out. The candidate structures were obtained by density functional theory calculations.